In optical fiber communication systems, it is often necessary to selectively switch the optical transmission emanating from one optical waveguide between alternative waveguides. Many arrangements exist for providing this type of switching.
U.S. Pat No. 4,239,331 discloses an optical switch that moves an angularly-orientated transparent plate into, and out of, the optical path between pairs of fibers on opposite sides of the plate. The signal passes through a collimating lens as it enters the switch. If the plate is not in the optical path, the signal passes to a second lens element, opposite the first element, that focuses the signal on the end of an optical fiber. If the plate is within the optical signal path, the signal path is altered by refraction into a different lens element which focuses the light on the end of another optical fiber.
U.S. Pat. No. 4,932,745 discloses an optical switch utilizing a refracting slab that is moved parallel to its sides into the path of the optical signal in order to select a different output fibers. Lens elements collimate the optical signal prior to its passing through the slab and focus the signal after being refracted, as in the '331 patent.
U.S. Pat. No. 5,000,534 discloses an optical switch that utilizes a movable planar mirror for switching the optical signal between pairs of fibers by reflection. The optical signal is collimated by a lens and then reflected by the mirror onto a second lens which focuses the signal onto an end of another optical fiber. Switching occurs by changing the angular orientation of the mirror, thereby selectively reflecting the signal through another focusing lens onto a different optical fiber.
U.S. Pat. No. 4,329,017 discloses an optical switch that uses a movable spherical reflector to effectuate switching of optical signal. Switching occurs by tilting the spherical surface so that its center of curvature is midway between the end of the fiber from which the signal emanates and the end of the fiber receiving the signal.
In the first three patents, the inventions require the use of collimating and focusing lenses in conjunction with a mirror or a refractive element. In the final patent, a movable concave reflective mirror is used without lens elements but the center of curvature of the mirror surface must be precisely located in relation to the ends of the waveguides. This alignment is especially difficult to maintain when using single mode optical fibers.
What is needed is a compact optical signal switch that may be used with single mode signal transmissions that utilizes a minimum number of precision optical components and is adjustable to compensate for optical element misalignment during assembly and set-up, thereby allowing for the use of less precisely manufactured components.